1. Field of the Invention
The present invention relates to chitosan salts having improved absorbent properties. Specifically, the present invention relates to chitosan salts having an improved ability to absorb liquid while under an external pressure and a process for the preparation thereof.
2. Description of the Related Art
The use of water-swellable, generally water-insoluble absorbent materials, commonly known as superabsorbents, in disposable absorbent personal care products is known. Such absorbent materials are generally employed in absorbent products such as diapers, training pants, adult incontinence products, and feminine care products in order to increase the absorbent capacity of such products while reducing their overall bulk. Such absorbent materials are generally present in absorbent products in a fibrous matrix, such as a matrix of wood pulp fluff. A matrix of wood pulp fluff generally has an absorbent capacity of about 6 grams of liquid per gram of fluff. The absorbent materials described above generally have an absorbent capacity of at least about 10, preferably of about 20, and often of up to 100 times their weight in water. Clearly, incorporation of such absorbent materials in personal care products can reduce the overall bulk while increasing the absorbent capacity of such products.
A wide variety of materials has been described for use as absorbent materials in such personal care products. Such materials include natural-based materials such as agar, pectin, gums, carboxyalkyl starch, and carboxyalkyl cellulose, as well as synthetic materials such as polyacrylates, polyacrylamides, and hydrolyzed polyacrylonitrile. While the natural-based absorbent materials are known for use in personal care products, they have not gained wide usage in such products. The natural-based absorbent materials have not gained wide usage in personal care products, at least in part, because their absorbent properties are generally inferior compared to the synthetic absorbent materials, such as the polyacrylates. Specifically, many of the natural-based materials tend to form soft, gelatinous masses when swollen with a liquid. When employed in absorbent products, the presence of such soft gelatinous masses tends to prevent the transport of liquid within the fibrous matrix in which the absorbent materials are incorporated. This phenomenon is known as gel-blocking. Once gel-blocking occurs, subsequent insults of liquid cannot be efficiently absorbed by the product, and the product tends to leak. Further, many of the natural-based materials exhibit poor absorption properties, particularly when subjected to external pressures.
Chitosan, a deacetylated chitin, is a cation-active, poly-primary amine with diverse applications in fields such as dispersing agents, adhesives, pesticides, waste water treatment, food processing, and wound healing.
Unfortunately, the known modified chitosan materials generally do not possess absorptive properties comparable to many of the synthetic, highly-absorptive materials. This has prevented widespread use of such chitosan materials in absorbent personal care products.
In contrast, the synthetic absorbent materials are often capable of absorbing large quantities of liquid while maintaining a generally stiff, non-mucilaginous character. Accordingly, the synthetic absorbent materials can be incorporated in absorbent products while minimizing the likelihood of gel-blocking.
It is therefore desirable to develop and produce a natural-based, highly absorbent chitosan material having absorptive properties similar to the synthetic, highly absorptive materials and, thus, suitable for use in personal care absorbent products.